Field of the Invention
The present invention relates to a charged particle beam system.
Description of Related Art
In an electron microscope or charged particle beam system (such as a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), or a scanning electron microscope (SEM)), an electron microscope image is obtained by irradiating a sample with an electron beam and detecting secondary electrons emitted from the sample, backscattered electrons, electrons transmitted through the sample, or scattered electrons.
In an electron microscope, when a sample is irradiated with an electron beam, contaminant materials adhering to the surfaces of the sample and of a sample stage interact with the electron beam. This may contaminate the sample surface. It is said that the contaminant materials are carbon-based molecules. If the surface of the sample is contaminated, intrinsic image contrast attributed to the sample cannot be easily derived. Furthermore, if the sample surface is contaminated during an analysis, such as electron dispersive spectroscopy (EDS) analysis or electron energy loss spectroscopy (EELS) analysis, signals not stemming from the sample may be detected and appear as system peaks.
In an attempt to suppress sample contamination as described above, JP-A-2009-266697, for example, discloses a technique for nondestructively cleaning the vacuum paths of an electron microscope by introducing active oxygen radicals into the vacuum paths.
Another technique for suppressing sample contamination is also known. In this technique, a sample and a sample stage on which the sample is secured are cleaned by the use of a cleaning device (i.e., sample contamination preventive device) prior to observation or analysis of the sample using an electron microscope. In this cleaning device, a plasma is directed onto the sample and the sample stage to etch their surfaces. Consequently, contaminant materials adhering to the surfaces of the sample and sample stage can be removed. During the plasma irradiation, the etching rate can be enhanced by introducing an inert gas such as Ar gas.
Where the above-described cleaning device is used, however, when the sample is transported into the sample chamber of the electron microscope from the cleaning device after cleaning the sample, the sample must be temporarily exposed to the atmosphere, which contains contaminant materials in quantity. When a sample is exposed to the atmosphere, the contaminant materials may adhere to the sample surface again, thus reducing the effect of suppressing sample contamination.